What is the irony in Macbeth's soliloquy in Act 3 Scene 1? "To be thus is nothing,But to be safely thus. Our fears in Banquo Stick deep, and in...

Macbeth's soliloquy is full of contrasts, as he struggles with incredulity that becoming king has not brought him security or happiness and instead he has a constant fear of Banquo and his sons as successors. There are several small ironies that come into play here.

One is that the very prophesy that excited Macbeth and led him to murder, now terrifies him and has him fearing for his own life. The cognitive dissonance that allowed...

Macbeth's soliloquy is full of contrasts, as he struggles with incredulity that becoming king has not brought him security or happiness and instead he has a constant fear of Banquo and his sons as successors. There are several small ironies that come into play here.

One is that the very prophesy that excited Macbeth and led him to murder, now terrifies him and has him fearing for his own life. The cognitive dissonance that allowed Macbeth to believe the witches when they said he would be king but not worry about their prophesy that Banquo's sons would rule is now catching up to him here.

Additionally, the thing that makes Banquo such a fearsome opponent is "his royalty of nature" (3.1.52), which makes him both daring and clever enough to pull of an attempt on Macbeth's life. Of course, the word choice also suggests that Banquo would be a worthy king, in which case perhaps Macbeth should stand aside and let him rule, if he is as wise and clever as Macbeth claims.

Finally, the word choice of this soliloquy has contrasts in it, particularly the pronouns: 

"They hailed him father to a line of kings.
Upon my head they placed a fruitless crown
And put a barren scepter in my grip (3.1.63-5) [Emphasis mine]

Macbeth struggles with the seeming pointlessness of killing Duncan to become king when he has no sons and heirs to carry on his crown. In the line, "To make them kings, the seed of Banquo kings!" (3.1.73), he seems furious and astounded at the absurdity that he would go through all that trouble only for Banquo's sons to rule. Again, though, most audience members would point out that he should have considered this before killing Duncan.